• A pronoun substitutes a noun or a noun phrase, with or without a determiner: it, this. • A pro-adjective substitutes an adjective or a phrase that functions as an adjective: so as in "It is less so than we had expected." • A pro-adverb substitutes an adverb or a phrase that functions as an adverb: how or this way. • A pro-verb substitutes a verb or a verb phrase: do. • A pro-sentence substitutes an entire sentence or subsentence: Yes or (some have argued) that as in "That is true."